[Linux-cachefs] [PATCH 1/2] netfs: refactor arguments for netfs_alloc_read_request

[David Howells]

Below is my take on this.  I've moved it earlier in the patchset, so some bits
have migrated to other patches.

---
commit b32c31951d58c605a0993da59de0132cb5ef0723
Author: Jeff Layton <jlayton at kernel.org>
Date:   Thu Aug 26 09:24:42 2021 -0400

    netfs: refactor arguments for netfs_alloc_read_request
    
    Pass start and len to the rreq allocator. This should ensure that the
    fields are set so that init_rreq can use them.
    
    Also add a parameter to indicates the origin of the request.  Ceph can use
    this to tell whether to get caps.
    
    Signed-off-by: Jeff Layton <jlayton at kernel.org>
    Signed-off-by: David Howells <dhowells at redhat.com>

diff --git a/fs/netfs/read_helper.c b/fs/netfs/read_helper.c
index b4122653c259..19eb114ebf2a 100644
--- a/fs/netfs/read_helper.c
+++ b/fs/netfs/read_helper.c
@@ -29,8 +29,11 @@ MODULE_PARM_DESC(netfs_debug, "Netfs support debugging mask");
 static void netfs_rreq_work(struct work_struct *);
 static void netfs_rreq_clear_buffer(struct netfs_read_request *);
 
-static struct netfs_read_request *netfs_alloc_read_request(struct address_space *mapping,
-							   struct file *file)
+static struct netfs_read_request *netfs_alloc_read_request(
+	struct address_space *mapping,
+	struct file *file,
+	loff_t start, size_t len,
+	enum netfs_read_origin origin)
 {
 	static atomic_t debug_ids;
 	struct inode *inode = file ? file_inode(file) : mapping->host;
@@ -39,8 +42,11 @@ static struct netfs_read_request *netfs_alloc_read_request(struct address_space
 
 	rreq = kzalloc(sizeof(struct netfs_read_request), GFP_KERNEL);
 	if (rreq) {
+		rreq->start	= start;
+		rreq->len	= len;
 		rreq->mapping	= mapping;
 		rreq->inode	= inode;
+		rreq->origin	= origin;
 		rreq->netfs_ops	= ctx->ops;
 		rreq->i_size	= i_size_read(inode);
 		rreq->debug_id	= atomic_inc_return(&debug_ids);
@@ -1026,11 +1032,12 @@ void netfs_readahead(struct readahead_control *ractl)
 	if (readahead_count(ractl) == 0)
 		return;
 
-	rreq = netfs_alloc_read_request(ractl->mapping, ractl->file);
+	rreq = netfs_alloc_read_request(ractl->mapping, ractl->file,
+					readahead_pos(ractl),
+					readahead_length(ractl),
+					NETFS_READAHEAD);
 	if (!rreq)
 		return;
-	rreq->start	= readahead_pos(ractl);
-	rreq->len	= readahead_length(ractl);
 
 	ret = netfs_begin_cache_operation(rreq, ctx);
 	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS)
@@ -1091,11 +1098,10 @@ int netfs_readpage(struct file *file, struct page *subpage)
 
 	_enter("%lx", folio_index(folio));
 
-	rreq = netfs_alloc_read_request(mapping, file);
+	rreq = netfs_alloc_read_request(mapping, file, folio_file_pos(folio),
+					folio_size(folio), NETFS_SYNC_READ);
 	if (!rreq)
 		goto nomem;
-	rreq->start	= folio_file_pos(folio);
-	rreq->len	= folio_size(folio);
 
 	ret = netfs_begin_cache_operation(rreq, ctx);
 	if (ret == -ENOMEM || ret == -EINTR || ret == -ERESTARTSYS) {
@@ -1272,7 +1278,8 @@ int netfs_write_begin(struct file *file, struct address_space *mapping,
 	}
 
 	ret = -ENOMEM;
-	rreq = netfs_alloc_read_request(mapping, file);
+	rreq = netfs_alloc_read_request(mapping, file, folio_file_pos(folio),
+					folio_size(folio), NETFS_READ_FOR_WRITE);
 	if (!rreq)
 		goto error;
 	rreq->start		= folio_file_pos(folio);
diff --git a/include/linux/netfs.h b/include/linux/netfs.h
index cd572bf1dfa3..210f9414747c 100644
--- a/include/linux/netfs.h
+++ b/include/linux/netfs.h
@@ -168,6 +168,12 @@ struct netfs_read_subrequest {
 #define NETFS_SREQ_NO_PROGRESS		4	/* Set if we didn't manage to read any data */
 };
 
+enum netfs_read_origin {
+	NETFS_READAHEAD,		/* This read was triggered by readahead */
+	NETFS_SYNC_READ,		/* This read is a synchronous read */
+	NETFS_READ_FOR_WRITE,		/* This read is to prepare a write */
+} __mode(byte);
+
 /*
  * Descriptor for a read helper request.  This is used to make multiple I/O
  * requests on a variety of sources and then stitch the result together.
@@ -186,6 +192,7 @@ struct netfs_read_request {
 	size_t			submitted;	/* Amount submitted for I/O so far */
 	size_t			len;		/* Length of the request */
 	short			error;		/* 0 or error that occurred */
+	enum netfs_read_origin	origin;		/* Origin of the read */
 	loff_t			i_size;		/* Size of the file */
 	loff_t			start;		/* Start position */
 	pgoff_t			no_unlock_folio; /* Don't unlock this folio after read */